Composites Flashcards
(31 cards)
What is a composite?
A composite is a material that contains two or more distinct material as a unified combination.
How are composites classified?
By a constitution (what the material is made from), reinforcement form, spacial distribution, and relative proportions.
What are the types of reinforcement form?
Continuous filament/fibre, Short/discontinuous fibre, Particulate
What are the spacial distribution for continuous filament/fibres?
Uniaxial (high volume fraction of reinforcement), woven/ cross stitched (medium volume fraction of reinforcement), swirl mat (varying volume fraction).
What are the advantages of composites?
Enhanced and more control over mechanical, physical and chemical properties.
What are some possible reason why fibres are strong?
Molecular alignment, Crystallographic alignment, Elimination of flaws, Development of fine structures.
What are the main types of fibres?
Glass fibre, Carbon fibres, Polymer fibres and Ceramic fibres.
What are the benefits of glass fibres?
Provides good strength properties.
What is the difference between pan and pitch carbon fibres?
Pan are cost effective carbon fibres while pitch carbon fibres are highly thermal and electrically conductive.
What are the benefits and disadvantages of polyaramid fibres?
They have high stiffness, high toughness and low density but low compression strength and severe degradation in UV.
What are the benefits and disadvantages of ceramic fibres?
Handle high temperatures, chemical stable and high stiffness, but generally have a low strength.
What are the types of ceramic fibres?
Monofilaments, multifilament, short staple and whiskers.
What are monofilaments?
Single continuous strand of fibre.
What are multifilaments?
Multiple types of fine strands of fibres twisted together.
What are short staple fibres?
Short length fibres
What are whiskers fibres?
Very fine single crystal strand of fibres, with both high strength and high stiffness.
What are the general properties of fibres?
Fibres tend to be stiffer and anisotropic compared to the bulk counterparts.
What is the Weibull distribution?
Since strength is controlled by flaw distribution fibre strength varies on a statistical basis. Shorter length fibres are statistically stronger than longer fibres.
What is the polymer matrix?
A continuous phase that protects the fibre, carries shear stress and allows transmission of stress into fibres.
What are the processing requirements for a polymer matrix?
Low viscosity, Easy to shape, quality assurance, ideally rapid processing and long pot life.
What are the principle thermoset matrices for composites and their benefits?
1) Unsaturated polyester resin, Cheap, limited HT and chemical resistance.
2) Epoxy Resins, more expensive, but better HT and chemical resistance.
3) Vinyl-Ester Resins, intermediate HT and chemical resistance.
4) Phenolic, cheap and moderately mechanical
5) High Temperature Resins, For high temperature resins
What are the principle thermoplastic matrices for composites and there benifits?
1) Commodity moulding compounds, medium properties, cheap, good processibility.
2) Thermoformable sheet, more random commodity moulding compounds
3) Engineering thermoplastics, highest strength and HDT
4) High performance thermoplastics, very high Tg
What are the advantages of thermoplastics?
Processing is easier to control, recyclability, storage prior to processing, tougher, more moisture resistant.
What are the advantages of thermosets?
Lower processing temperatures, faster cycle times, better compression strength, better translation of fibre properties generally more solvent resistant.